1. Field of the Invention
The present invention relates to automatic rangefinder and focusing apparatus for use in cameras. The apparatus illuminates an object to be photographed with light that is modulated at a frequency that is functionally related to the distance from the object to the camera. A photoresponsive device receives light reflected from the object and analyzes its modulation frequency to derive a readout of the object distance and/or to focus the camera's objective lens.
2. Description of the Prior Art
Automatic camera rangefinder and focusing devices known in the prior art can be categorized broadly as either passive or active devices, the former being those which derive object distance information from ambient light reflected from the object to be photographed and the latter being those in which distance information is derived from light originating at the camera and reflected back to the camera by the object. The present invention relates to automatic rangefinder and focusing devices of the active type and, more particularly, to that type of device in which the object distance is determined by triangulation principles as a function of the angle between the axis of the path of light emitted from the camera and impinging on the object and the axis of the path along which such light is reflected back to a photodetector incorporated in the camera.
Automatic camera rangefinder and focusing devices of the above described triangulation type can also be classified into two general species, namely those employing multiple light sources or multiple photodetectors to sense the presence of an object within different distance zones and those in which the optical axis of a single photodetector or light source sweeps angularly through the complete distance zone within which the device is intended to function. The present invention relates to both of these species, typical examples of which are disclosed in U.S. Pat. No. RE. 27,461 entitled Automatic Focusing For Cameras and assigned to the same assignee as the present invention. In the zone type of device, the plural light emitters or plural photodetectors are operated sequentially to identify the distance zone within which the object is located. In a variation of this type of device, two adjacent optical paths of the light emitters or photodetectors define respective zones and can overlap to define a third zone. The scanning type of device employs a movable element to cause a sweeping motion of the emitted light beam or of the field of view of the photodetector, and determines the object distance as a function of the instantaneous angular position of that movable element when the reflected light from the object is received by the photodetector.
To minimize the possibility of spurious photodetector energization caused by ambient light, it is known in both the zone and sweep species of automatic triangulation type rangefinder and focusing devices to employ light sources of specific spectral or modulation frequency characteristics which are unusual in normal ambient light whereby correspondingly selective photoresponsive devices can distinguish the light emitted from the camera from light originating from other sources.